Subsea hydraulic couplings are old in the art. The couplings generally consist of a male and a female member with seals positioned within the female member to seal the junction between the male and female members.
The female member is generally a cylindrical body with a relatively large diameter longitudinal bore at one end and a relatively small diameter longitudinal bore at the other. The small bore facilitates connections to hydraulic lines, while the large bore contains the seals and receives the male portion of the coupling. The male member includes a cylindrical portion at one end having a diameter approximately equal to the diameter of the large bore in the female portion of the coupling. The male member also includes a connection at its other end to facilitate connection to hydraulic lines. When the cylindrical portion of the male member is inserted into the large bore of the female member, according to the various embodiments of the device, the seals, generally resembling 0-rings, either abut the end, or face, of the male member or engage the male member about its circumference. The hydraulic fluid is then free to flow through the female ad male portions of the coupling, and the seals prevent that flow from escaping about the joint in the coupling.
In some instances a check valve may be installed in the female member and also in the male member. Each check valve is opened when the coupling is made up; however, each check valve closes when the coupling is broken, so as to prevent fluid from leaking out of the system of which the coupling is a part.
The seals most commonly used in the past have been of an elastomeric material and such seals have numerous disadvantages. The principal disadvantages are (1) the inability of the seal to withstand the deteriorating effects of a subsea environment for extended periods of time, and (2) the inability of the soft seal to contain the higher pressures being imposed on the hydraulic systems.
Metal seals have been developed to better withstand both the deteriorating effects of the environment and the higher pressures. One such seal is a crush-type which is positioned between the end of the male portion of the coupling and the internal end of the large bore in the female portion. When the male portion is inserted into the female, the metal seal is crushed between the two portions and a seal is effectuated between the two. In view of the crushing action, the seal can be used only once. If the coupling is separated for any reason, the once-used crushed seal must be replaced with a new seal. Also, the male and female members must remain fully engaged to prevent leakage around the seal.
Another type of metal seal has been employed for sealing between the end face of the male member and a shoulder in the bore of the female member. This seal has a cavity which is exposed to pressure in the coupling and, in response to that pressure, the seal tends to expand longitudinally to effectuate the seal between the face of the male member and the shoulder in the female. This longitudinal expansion of the seal tends to force the male member out of the bore of the female member. To overcome the tendency for the male and female members to part, and to insure a sealing relationship of the seal with the male and female members prior to pressurization of the coupling, an external preload mechanism is used which holds the male and female members together. The drawback to this apparatus is that if the internal pressure exceeds the holding capacity of the external preload mechanism, the male and female members will part sufficiently to break the sealing relationship with the metal seal. Also, external preload mechanisms are expensive and require considerable space for mounting in a subsea environment. The complex mechanism affords greater possibility of problems and malfunctions.
The male and female portions of the above couplings are each one-piece devices, and the seal rests at the interior end of the female bore for engagement with the end of the male portion. Particularly in the case of the face-type seals, there is no mechanism for retention of the seal in the female section. If the coupling is parted under pressure, the seal will generally blow out of the female section and be lost. There may also be risk of injury to the operator parting the coupling.
Still another type of metal seal has been used between the male and female members of a coupling. A pressure energized annular seal has been used to seal between the side wall of the male member and the bore wall of the female member. That coupling and metal seal are shown in Applicant's pending application Serial No. 801,477, filed November 25, 1985. The annular metal seal is trapped within the female body by means of a retainer which traps the seal against a shoulder inside the female member. The probe, or male member, is designed to be inserted through the retainer and through the metal seal so that the seal engages the circumference of the probe in a sealing relationship. A cavity in the seal is exposed to the internal coupling pressure to enhance the effectiveness of the seal.